1. Field of the Invention
The present invention relates to a method for producing a Group III nitride semiconductor light-emitting device exhibiting improved light extraction performance.
2. Background Art
A method for providing a concave and convex configuration on a light output surface has been proposed to improve the light extraction performance of the Group III nitride semiconductor light-emitting device.
In a known method for providing a concave and convex configuration, a reversed polarity layer is used. A Group III nitride semiconductor is usually grown in a +c axis direction and thus has a Group III element polarity. However, a reversed polarity layer includes at least a portion thereof with a nitrogen polarity opposite to a Group III element polarity. The reversed polarity layer can be formed by doping a high concentration of Mg into the crystal. (For example, refer to Japanese Patent Application Laid-Open (kokai) No. 2003-101149.)
Japanese Patent Application Laid-Open (kokai) No. 2009-49395 discloses that a p-GaN layer is formed on a p cladding layer, a reversed polarity layer is formed on the p-GaN layer, and a concave and convex configuration is formed by wet etching the reversed polarity layer, that is, an area with a nitrogen polarity.
In Japanese Patent Application Laid-Open (kokai) No. 2010-62493, a reversed polarity layer is formed on a p-type first semiconductor layer comprising a Group III nitride semiconductor with a Group III element polarity. On the reversed polarity layer, a p-type second semiconductor layer comprising a Group III nitride semiconductor with a nitrogen polarity is formed, and a concave and convex configuration is formed by wet etching the surface of the second semiconductor layer. It is also disclosed that the first semiconductor layer with a Group III element polarity functions as an etching stopper to prevent the second semiconductor layer from being excessively etched.
Other known methods include a method for providing a concave and convex configuration through processing or a method utilizing steps formed by the step growth on a substrate having a large off-angle.
However, the methods disclosed in Japanese Patent Application Laid-Open (kokai) Nos. 2009-49395 and 2010-62493 require at least a process for forming a reversed polarity layer and a process for wet etching. Therefore, the production is complicated due to multiple processes, resulting in an increase of the production cost.
A method for providing a concave and convex configuration through processing requires a specific process after crystal growth, resulting in an increase of the production cost. In addition, some crystal damage remains and a special etching is required because the Group III nitride semiconductor has high hardness. A p-contact layer being the top surface needs to be thick for processing. However, a p-type Group III nitride semiconductor is difficult to be grown thick while maintaining a good crystallinity.
In a method utilizing the step growth, a concave and convex configuration is formed on all layers being deposited on a substrate. This may reduce the steepness of the interface and degrade the light emission performance. When the off-angle of the substrate is increased, there is a problem that crystallinity is considerably reduced.